An experimental study on the effects of injection-molding types for the birefringence distribution in polycarbonate discs

Abstract

Even though injection molding technology has been developed for many years, it is still needed to study the effect of processing conditions on the final properties of injection-molded parts for producing precision products in optical field. The optical anisotropy, i.e., birefringence, is a significant factor which affects the function of many optical components. In the present study, we have focused on the effects of packing and compression processes on the birefringence structure remaining in the disc by examining the gap-wise distribution of birefringence and extinction angle. As a result, two extra birefringence and extinction peaks near the center in thickness direction showed the effect of packing pressure, which came from the extra flow during packing stage. Furthermore, more uniform birefringence distribution was found in injection/compression case than in conventional injection-molded case. Depending on the process condition, even the reversal flow was found from the distribution of extinction angle in injection/compression case. Finally, graphical representation technique of optical refractive indicatrix was suggested to show the difference of final birefringence structure for different process types.

Effects of adding injection–compression to rapid heat cycle molding on the structure of a light guide plate

“…Guan and Huang [27] simulated the influence of back flow in ICM on thickness distribution. Similarly, Min and Yoon [29] found reversal of extinction angle far from the gate in their experimental analyses of optical disc data. In this study, the mold geometry is responsible for the back flow near the gate.…”

Research on Continuous Injection Direct Rolling Process for PMMA Optical Plate

“…As can be seen from Figure 19, the birefringence of the sample is small near both sides and it is the largest in the middle. But all the values of birefringence are small compared with other methods [14]. According to the light elastic theory, birefringence is related to residual stress in the optical material [15], so the residual stress in the sample is small.…”

Overview of Injection Molding Technology for Processing Polymers and Their Composites

“…The actual effective maximum dwell time will remain the same, and the haze will not change. Min et al [77] studied the influence of the filling and compression processes on the residual birefringence structure of the optical disc by testing the birefringence distribution and the extinction angle. Two anomalous birefringence and extinction peaks near the center in the thickness direction indicate the holding pressure, which indicates that the holding pressure has a certain effect when the flow is replenished during the holding phase.…”